[mr48chev]

That 49 cab actually has what should be the original recirculating air heater.

As far as I know they only came from the factory with the "fresh air" heater that connects to the side so it draws fresh air in though the louvers in the side of the cowl and the recirculating air heater like this one.

The block off plate for the heater motor off that firewall is on my 48 after I pulled the heater out of it due to the core leaking. I'm thinking that a cap for one or more of the other heater tube openings may have been taken off before I got the cab. A friend gave it to me about 30 years ago and I have drug it around ever since.

A big number of AD trucks were shipped from the factory without heaters. That kept the price down a few bucks and on the big trucks a lot of them only got used a couple of months a year for harvest when they didn't need a heater. A lot of AD trucks in Florida, south Texas, southern New Mexico and Arizona have never had heaters in them.

The 51 1-1/2 ton I have has a square aftermarket heater that was either installed by the dealer or by an owner at some time. Dealers would often put in what they had on the shelf in the back room including heaters for older Chevy cars or trucks.

Most of the square heaters were aftermarket from a parts house. You went down and bought one from the local parts house and took it back and installed it.

Then there was what ever you could find at the wrecking yard that fit and didn't leak. Around here you never know what You will find in one as quite often the farmers were pretty cheap and resourceful.